A prior art programmed control process of a system for numerically controlling a machine tool with the use of an electronic computer is illustrated in FIG. 1. Either the signal P.sub.a from a tape reader 5 or the signal from an electronic computer 6 is selectively supplied to a numerical control (NC) circuit 2 for a machine tool 1. The data are exchanged through transmission lines between the numerical control circuit 2 and the machine tool 1. A manual data inputting panel (MDIP) 3 (alternatively designated "manual data panel" hereinafter) provided in the numerical control circuit 2 receives an input signal M.sub.a from an operator and sends an output signal M.sub.b to the operator.
However, in order to carry out a program control with the use of said computer 6 in the system of FIG. 1, it is necessary to obtain the input signal D.sub.i from the machine tool 1 and the output signal D.sub.o for the machine tool 1 which are being exchanged between the numerical control circuit 2 and the machine tool 1, and the signals M.sub.a and M.sub.b which are applied to and displayed at the manual data inputting panel 3, and then to have the computer operate on the basis of the obtained data. Such processes in the system of FIG. 1 have been inconvenient and unsatisfactory from the viewpoint of the performance of an automatic programmed control of the system.